Impact of Height-to-Mass Ratio on Physical Fitness of German Third-Grade Children

Abstract

Physical fitness (PF) is closely related to body constitution, with either height-to-mass ratio (HMR) or body mass index (BMI) as indicators. We compared these indicators for 24,777 third-grade children from 2017–2022 cohorts in cardiorespiratory endurance (6-min run), coordination (star-run), speed (20-m sprint), lower- (standing long jump) and upper limb (ball-push test) muscle power, and static balance (one-legged-stance test; eyes closed). Quadratic HMR predicts children’s physical fitness better than cubic BMI after adjustment for secular trends and the COVID-19 pandemic effects on PF. Except for powerUP, PF scores decreased with increasing body mass relative to height (low HMRs). Boys outperformed girls in five tests (exception balance), but their performance losses were larger with increasing overweight. Surprisingly, after adjustment for quadratic HMR trends, the main effects of sex favored girls (exception powerUP). We propose children’s motor performance, usually normed with age- and sex-specific categories, should be assessed with body height-to-mass ratio.